A multi-subscription multi-standby (MSMS) device may include two or more subscriber identity module (SIM) cards, each associated with a different service provider subscription. An MSMS communication device may support a range of communication technologies and configurations, including both cellular and Wi-Fi. For example, in an MSMS communication device (for example, a Dual-SIM Dual-Standby (DSDS) device), two or more SIMs share one radio. In contrast, in a multi-subscription multi-active (MSMA) device (for example, a Dual-SIM Dual-Active (DSDA) device), two or more SIMs may establish two or more concurrent communication sessions using two or more radios. MSMS devices and MSMA devices may use different radio access technology (RAT) protocols with different subscriptions. Such RATs may include 3GPP Long Term Evolution (LTE), Global System for Mobility (GSM), Single-Carrier Radio Transmission Technology (1×RTT), and others.
Many times an end-user device may be connected with a Wi-Fi access point (e.g., in the office or at home). Conventional MSMS communication devices conducting a Voice over Wi-Fi (also referred to as Wi-Fi Calling, or WFC) using a first subscription may be unable to monitor a second subscription for paging messages, or cannot enter into an active state and identify the caller party number to perform a call switch to an incoming call (e.g., that may be indicated by a paging message). A network operator may enable WFC on a network, which enables the switching of Voice over LTE (VOLTE) or Video Telephony (VT) calls to Wi-Fi (connected through an Evolved Packet Data Gateway (ePDG) backend to an IP Multimedia System (IMS) core) when Wi-Fi is available. However, while many network operators are enabling WFC, in many current communication device designs (e.g., in DSDS devices), the modem and the telephony layer have not been designed to monitor for a paging message over another subscription. Current communication devices have also not been designed to receive incoming voice calls over another subscription while the device conducts an active voice call over WFC.
So, for example, an MSMS communication device may prevent a tuning of its radio frequency (RF) resource away from the first subscription (that is conducting a voice call) to a second subscription to conduct an active communication session on the second subscription. The MSMS communication device may therefore not respond to one or more paging messages sent from the communication network of the second subscription when the MSMS communication device is conducting an active communication session on the first subscription using WFC. For example, with reference to FIG. 1A, in current LTE+GSM/1×RTT (LTE+G/1×) DSDS design, when a communication device (e.g., communication device 102a) conducts an active voice call using WFC using a first subscription on a first communication network (e.g., via access point 108a), the communication device 102a may monitor 1×/G paging messages on a second subscription (e.g., via base station 104a), but the communication device 102a cannot setup the call on the subscription or determine the caller's identity. As a result, important calls may be missed. As another example, with reference to FIG. 1B, when a communication device (e.g., communication device 102b) conducts a voice call using 1×/G on a second subscription (e.g., via the access point 108b), the communication device 102b may not be designed to set up a call over the first subscription (e.g., if the call is in WFC) assuming that radio frequency (RF) chains of the communication device 102b are dedicated for use by second subscription voice calls (e.g., as in a traditional DSDS device design). Again, important calls may be missed.